MySql查询根据价格获得类似的结果

Question

Don't know if the title for this question is ok, but my problem is simple.
I have a list of results and for simplicity, it contains only an id and a price :

+----+-------+
| id | price |
+----+-------+
| 11 |   10  |
| 52 |   17  |
| 23 |   45  |
| 24 |   50  |
| 55 |   60  |
| 96 |   70  |
|  7 |   75  |
| 78 |   80  |
| 99 |   100 |
+----+-------+

For a given id/price, I need to find first 2 records with a lower price and next 2 with a higher price.

For example, for id = 55 and price = 60, the results would be:

+----+-------+
| id | price |
+----+-------+
| 23 |   45  |
| 24 |   50  |

| 96 |   70  |
|  7 |   75  |
+----+-------+

In a rough implementation, this can be of-course obtained with a UNION, like this:

SELECT id, price
FROM MyTable
WHERE price <= 60 AND id != 55
ORDER BY price DESC
LIMIT 0,2

UNION ALL

SELECT id, price
FROM MyTable
WHERE price >= 60 AND id != 55
ORDER BY price ASC
LIMIT 0,2

But given the fact that MyTable is actually a view, obtained using a complex query behind, is there another way to achieve this?

I was even thinking that instead of running the query twice (with the UNION), to get all the results in one query and then to use PHP to find the 4 results.

Answer 1

You have to check this: Your query

SELECT id, price FROM (
SELECT @rank:=@rank+1 AS rank, @selectedRank := IF(id = 55, @rank,
@selectedRank), id, price
  FROM ( SELECT id, price FROM MyTable ORDER BY price
  ) t1, (SELECT @rank:=0) t2, (SELECT @selectedRank:=0) t3
) results
WHERE rank != @selectedRank AND rank BETWEEN @selectedRank - 2 AND @selectedRank + 2;

And this is what query explain shows: And this is another one:

SELECT * FROM test.mytable
WHERE
price >= (SELECT price FROM MyTable
    WHERE price <= 60
    ORDER BY price DESC
    LIMIT 2,1)
 and id != 55
ORDER BY price
LIMIT 4;

Which Query explain shows for it:

Answer 2

Thanks to @David Packer's hint and to this link , I found the solution to iterate the table only once:

SELECT id, price 
FROM (
  SELECT @rank:=@rank+1 AS rank, @selectedRank := IF(id = 55, @rank, @selectedRank), id, price
  FROM (
    SELECT id, price
    FROM MyTable
    ORDER BY price
  ) t1, (SELECT @rank:=0) t2, (SELECT @selectedRank:=0) t3
) results
WHERE rank != @selectedRank
AND rank BETWEEN @selectedRank - 2 AND @selectedRank + 2;